The present invention relates to photocurable silicone fluid compositions having an enhanced rate of photocure. More particularly, the present invention relates to polydiorganosiloxane fluids having chloroalkyl radicals and epoxyalkyl radicals attached to silicon by carbon-silicon bonds; the fluids exhibit improved compatability with polyarylhexafluoro onium salt photocatalysts, such as diaryliodoniumhexafluoro(Group VA.) salts when applied onto an appropriate substrate; these photocurable silicone fluid compositions can form valuable release coatings when photocured.
Epoxy functionalized polydiorganosiloxane fluids have been found useful for imparting improved release characteristics to various substrates, such as glass, plastic, or paper, when applied and cured thereon as shown by U.S. Pat. Nos. 4,421,904 and 4,927,158. Epoxy functionalized fluorosilicones, are shown by Eckberg et al U.S. Pat. No. 5,178,959, when photocured, are solvent-resistant coatings. Epoxy functionalized polydiorganosiloxane fluids can be photocured using a diaryliodonium salt, or "onium salt" catalyst. Experience has shown however, that the onium salt catalyst and epoxy functionalized polydiorganosiloxane fluid are often incompatible.
As taught in U.S. Pat. No. 4,264,703, compatability between an aromatic iodonium salts, such as diphenyliodoniumhexafluoroantimonate, and an epoxy functionalized silicone fluid can be enhanced, if the diaryliodonium salt has aryl radicals substituted with from 1-4 C.sub.(4-20) organo radicals. An additional method for enhancing onium salt- epoxy functionalized silicone fluid miscibility is by incorporating polyether blocks in the epoxy functionalized silicone fluid backbone, as shown in U.S. Pat. Nos. 5,227,410 and 5,240,971. However, the photocure efficiency of the resulting curable silicone mixture is sometimes adversely affected, as a result of the basicity of the incorporated polyether groups.
The present invention is based on the discovery that improved compatability between the onium salt and the epoxy functionalized silicone fluid can be achieved while avoiding a photocure response reduction, if the epoxy functionalized silicone fluid also incorporates an effective amount of chemically combined siloxy units having chloroalkyl radicals attached to silicon by carbon-silicon bonds. Surprisingly, the chloroalkyl modified epoxy functionalized silicone fluid also does not experience a significant denigration of release performance after it has been photocured on an appropriate substrate.